Karabiners are safety devices which are used to connect components in safety critical systems, particularly, but not exclusively in mountaineering and abseiling and which are also used in military applications and in industrial rope access work on sites and in situations where safety is critical, such as working at heights.
While there are a number of different designs of karabiners, they generally comprise a metal ring which will typically be oval, D-shaped, or pear shaped, along one side of which there is a hinged gate portion, which is typically spring loaded, so that movement of the free end of the gate portion opens the ring to allow a rope, webbing or the like to be inserted inside the ring. While some karabiners are non-locking and simply provide a sprung gate, most karabiners, include some means of locking the gate in the closed position.
In one common locking karabiner design (referred to as a “screwgate”) a threaded sleeve is provided for screwing over the free end of the gate portion to lock the gate closed.
The problem with the above design is that, in use, the threaded sleeve can move by frictional contact with other equipment, by vibration, or through inadequate tightening of the sleeve. Various changes have been proposed to the basic karabiner design to address the problem of the threaded sleeve coming undone.
“Twistlock” karabiners are one attempted solution to the problem. These karabiners include a sliding locking sleeve which is spring loaded and biased into the locking position, until the operator grasps and twists and pulls on the locking sleeve to disengage the free end of the gate. Twistlock karabiners are automatically locking and as soon as the operator releases the locking sleeve, it twists back into place to lock the gate. These are very difficult to use one handed and do not lock when exposed to grit which stops the spring from working When materials rub on the twistlock they can come undone very rapidly without warning.
“Ball-lock” karabiners are also known. In the case of these devices the operator must press a ball pin in order to turn the sleeve. While Twistlock and ball-lock karabiners can be more reliable than screwgate karabiners, the more complex design is less reliable particularly in adverse conditions (e.g. cold, snow ice etc . . . ), and more particularly cannot be operated using one hand, which is a major disadvantage in many applications where the operator may be hanging, and only have one free hand.
“Magnatron” karabiners are also known. These have two small levers with embedded magnets on either side of the locking gate which must be pushed or pinched simultaneously to disengage. Upon release, the levers pull shut and into the locked position against a small steel insert in the nose of the karabiner. With the gate open the magnets in the two levers repel each other so they do not lock or stick together, which might prevent the gate from closing properly. These type of karabiner have the advantages of one-handed operation, and re-engaging without additional user input. However they have mechanical parts that can fail however and are less reliable in adverse conditions.
The same problems which occur with screwgate karabiners also apply to maillons, which have a threaded sleeve which tightens over a thread, as opposed to the hinged gate of a karabiner. Maillons can be stronger than karabiners but are more difficult to use. They tend to be used for making more permanent connections.
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